If Apes Go Extinct, So Could Entire Forests

http://blogs.scientificamerican.com/extinction-countdown/2015/03/11/if-apes-go-extinct-trees/

By John R. Platt | March 11, 2015

bonobos eat a lot of fruit, and fruit contains seeds. Those seeds travel through a bonobo’s digestive system while the bonobo itself travels through the landscape. A few hours later, the seeds end up being deposited far from where the fruits were plucked. And that, ladies and gentlemen, is where new trees come from.

But what if there were no apes? A new study published February 27 in the journal Oryx found that many tree and plant species in the Democratic Republic of the Congo rely almost exclusively on bonobos for seed dispersal. In the LuiKotale forest, where the study was conducted, 18 plant species were completely unable to reproduce if their seeds did not first travel through a bonobo’s guts. According to the paper if the bonobos disappeared, the plants would also likely go extinct.

The research, by biologist David Beaune of the Max Planck Institute for Evolutionary Anthropology, found that bonobos have a pretty amazing role in the forest. They eat for about 3.5 hours every day and travel a mean of 1.2 kilometers from meal sites before defecating and depositing the seeds that have passed through their systems. And we’re not talking about a small number of seeds: Previous research has estimated that an astonishing 11.6 million seeds travel through an average bonobo’s guts during its lifetime.

The bonobo has two major functions here. First of all, many seeds will not germinate well unless they have been “handled” (as scientists call it) by another species. Stomach acids and intestinal processes weaken a seed’s tough external coating, making it more able to absorb water and later sprout.

Secondly, many seeds won’t succeed if they remain too close to their parental trees. Beaune found that the seeds that fell to the ground near their parents either did not germinate or the seedlings did not survive because they were choked off by the nearby mature plants. For example, Beaune found that Guinea plum (Parinari excelsa) seeds that fell near their parent trees sprouted pretty well into seedlings but all such young plants died off before they could reach the sapling stage. Most other tree seeds from other species didn’t even sprout.

According to Beaune, no other species in LuiKotale have travel patterns sufficient to serve the same dispersal service as bonobos. Several monkey species do eat the same fruits, but they stay close to home and therefore don’t fill the same ecological role.

Unfortunately, bonobos face a constant threat of poaching for the bushmeat trade, putting them at risk of extinction in many parts of their range. If the bonobos disappeared from LuiKotale or any of their other habitats, that could create a cascading extinction cycle. Not only would the trees disappear, but so could many of the other species that also rely on the trees for food or shelter. It’s a condition known as “empty forest syndrome”—the forest itself may still exist, but its biodiversity levels will crash, leaving it a pale shadow of its former self.

Beaune’s study focused specifically on bonobos in a single forest, but he wrote that it has relevance to other ape species such as chimpanzees, gorillas and gibbons, all of which fulfill similar seed-dispersal roles. He suggested that conserving all ape species means also conserving trees, pollinators and the methods by which seeds disperse.